.responsive_video {
 max-width: 560px;
 height: 315px;
 width: 100%;
 resize: both;
}

.responsive_img {
 max-width: 100%;
 height: auto;
}

@media (max-width: 400px) {
 .exercice {
   width: 100%;
   min-width: 150px;
 }
}